1. Field of the Invention
The present invention relates to vibratory strings or music wire for musical instruments such as pianos, guitars, violins, violas and the like, and, in particular, to improved string materials for producing vibratory strings having improved harmonic, tonal and stability characteristics.
2. Description of the Related Art
Few musical experiences are more beautiful and fulfilling than listening to live music performed on an acoustic instrument such as a grand piano, guitar or violin. The tonal quality, tenor and intricate harmonics of traditional acoustic instruments have been unsurpassed even by the recent advent of modem digital/electronic sampling and reproduction techniques. However, as improvements and advancements in digital-electronic sound reproduction continue, more and more musicians and music hobbyists/enthusiasts are choosing to purchase and play digital electronic keyboard instruments and the like, rather than their acoustical (i.e., stringed) counterparts.
This shift in consumer preferences can be attributed largely to the relative low cost of such electronic instruments, the diversity of sound reproduction and amplification achieved and the ready portability of such instruments. However, another important consideration is that digital-electronic instruments, unlike their acoustic counterparts, generally do not require periodic tuning and maintenance.
Anyone who has owned or played an acoustic piano knows that it must be periodically tuned by a skilled technician in order to keep it in optimal playing condition. Acoustic pianos used for concert tour performances must be constantly tuned and retuned in order to keep the instruments in proper pitch and tune under a variety of ambient conditions. Even then, the pitch of the instrument is sometimes liable to drift if ambient conditions should change abruptly or if the instrument is not allowed adequate time to become acclimated to a new ambient environment. As a result of these inherent sensitivities to changing ambient conditions, and because of the large number of strings and other mechanisms involved, maintaining a concert grand piano in optimal pitch prior to and during a concert performance can be a vexing and time-consuming task.
A typical concert grand piano includes a plurality of longitudinally arranged vibratory strings or wires of varying length overlying a plurality of hammers. The number of strings per note will vary, depending upon the desired pitch of the note, i.e., typically one string per note in the lower octaves and two or three strings per note in the mid and upper octaves. Each string is vibrationally fixed or grounded at one end by a hitch pin located on the bowed portion of the piano harp and, at the other end, by an adjustable tuning pin frictionally and rotatably retained in a tuning (xe2x80x9cpinxe2x80x9d) block. The strings are placed under tension by turning or adjusting the tuning pin. The tensioned strings are thus capable of sustained vibration.
A sound board, typically formed from laminated or glued strips of a light hardwood such as spruce, is disposed underneath the tensioned strings for the purpose of acoustically amplifying the vibrations of the activated string or strings into audible sound. The sound board includes one or more bridges, typically of hard rock maple, on which each string bears down. The distance between the bridge and the tuning pin defines the active length of the string. The sound board is typically crowned such that it bows upward pressing the bridge (or bridges) into the taught strings. This improves the acoustic qualities of the piano and helps the sound board support the immense downward pressure brought to bear against it by the tensioned strings.
In operation, when a string (or strings) is struck by an associated hammer the string is set into mechanical vibration whereby a sound having a particular desired pitch is produced. The pitch depends largely upon the active length of the string, its weight or mass and the amount of tension applied. Thus, the shorter, smaller diameter strings located at the treble end of a piano typically produce a relatively high pitched sound whereas the longer, larger diameter strings disposed at the bass end of the piano produce a lower pitched sound. The tonal quality of the sound produced depends on a number of additional factors, such as the particular mechanical properties of the material or materials comprising the string, its ductility, tensile strength, modulus of elasticity, resistance to bending and density per unit length. Each of these properties can effect the tonal quality, tenor and dwell of a particular note, as well as the occurrence or selected amplification or attenuation of various harmonic partials.
For purposes of the present disclosure, a xe2x80x9cpartialxe2x80x9d is defined as a component of a sound sensation which may be distinguished as a simple sound that cannot be further analyzed by the ear and which contributes to the overall character of the complex tone or complex sound comprising the note. The fundamental frequency of the string is the frequency of the first partial, or that frequency caused by the piano string vibrating in the first mode, or the lowest natural frequency of free vibration of the string. A harmonic is a partial whose frequency is usually an integer multiple (e.g., n=1, 2, 3 . . . ) of the frequency of the first partial or fundamental frequency of the string.
Due to the nature of strings being strung and then tuned., strings for musical instruments are required to keep strong tension and a high degree of stability for a long period of time. Strings which plastically deform or stretch by bowing, plucking or striking are typically not used on musical instruments because they typically lack sufficient elastic compliance to sustain vibratory motion for any useful period of time and can also deform or permanently stretch if struck or plucked to hard.
Conventional vibratory strings used for pianos, electric guitars and similar musical instruments are typically made of materials having relatively high elastic modulus (greater than about 180 GPa), such as carbon steel wire, stainless steel wire, phosphor bronze wire and the like. Often a carbon steel wire core having a diameter of about 0.090 inches will be wound with annealed copper wire or other precious or semi-precious metals in order to change the density per unit length of the string and to enable optimal adjustment of sound quality, attenuation rate and selection of the basic vibration frequency. Thus, U.S. Pat. No. 5,578,775 to Ito describes a vibratory string for use on musical instruments comprising a core wire composed of long filaments of steel wire, sheathed with a thick mantle of a precious metal such as gold, silver, platinum, palladium, copper, or the like. U.S. Pat. No. 3,753,797 to Fukuda describes an improved string for a stringed instrument comprising carbon steel wire electrically heat treated under tensile stress to reduce residual stress in the string and thereby minimize tonal variation over long periods of time after the string has been strung in the instrument. For classical acoustic guitars, violins, violas, acoustic bases and similar instruments, a more compliant material may be chosen, such as cat gut, sheep gut or synthetic resins in order to achieve the desired tonal and acoustic qualities.
Notwithstanding the significant improvements made in vibratory string technology over the years, acoustic instruments remain quite sensitive to even small changes in temperature, humidity and other ambient conditions. Even a very small change in the stretch or amount of tension on a conventional vibratory string can result in significant detuning of the string. Such changes may result from, among other things, environmental conditions, such as temperature, humidity and the like, which may cause portions of the sound board, bridge and/or harp to expand or contract and thereby alter the string length/tension. These changes can cause the piano or other string instrument to produce a less than optimum sound, especially if rather large or frequent changes are experienced.
During the initial tuning of a piano or other stringed instrument by factory personnel, the tensioning or de-tensioning of the various strings can cause similar changes in the shape of the sound board, bridge and/or harp, particularly the degree of crowning of the sound board. The latter is directly affected by the total amount of downward pressure exerted on the sound board by the strings under tension. Thus, repeated iterative tunings at the factory over the course of several days or weeks are normally necessary to achieve a desired stable tonal range. The iterative nature of this initial tuning process and the large number of strings involved makes this an expensive and time-consuming process.
After a piano is put into service, periodic adjustment and maintenance by a skilled piano technician is required to keep the strings optimally tuned. As noted above, such tuning is carried out by rotating the various tuning pins, thereby either tightening or loosening each associated string. But, repeated adjustment of the tuning pins over years of use tends to adversely affect the tuning pins and/or the pin block in which they are frictionally retained. As a result, the pin block of an older piano will often become so worn by repeated tunings that the tuning pins no longer have sufficient frictional engagement with the pin block to prevent them from rotating under the stress of the tuned string. In such case the piano will not be able to hold its tune for prolonged periods and must either be tuned much more frequently or the pin block must be repaired or replaced.
But even with the piano properly tuned, it is still subject to certain inharmonicities which can adversely affect the tonal quality of the piano, particularly in the bass range. xe2x80x9cInharmonicityxe2x80x9d refers to the observed increase in the pitch of higher harmonic partials of a vibrating non-ideal string. Depending upon the physical and mechanical characteristics of the string material, these harmonic partials can sometimes vibrate at such elevated pitches that they produce disharmony with the fundamental and lower harmonic partials, causing unpleasant overtones. Undesirable overtones are particularly noticeable in the seventh, ninth and higher harmonic partials, especially in the lower range of the bass scale.
Conventionally, piano manufacturers have attempted to compensate for these unpleasant overtones and inharmonics by carefully selecting the strike point of the hammer so that it falls on or near a node of the partial harmonic(s) desired to be attenuated. See, for example, U.S. Pat. No. 4,244,268 to Barham. While such approaches are generally accepted to produce improved tonal quality, they have not been completely successful in removing all of the undesired disharmonic overtones. Rather, they are compromise approaches which attempt to attenuate as much as possible those disharmonic overtones that the human ear finds most unpleasant.
Accordingly, it is a principle object and advantage of the present invention to over-come some or all of these limitations and to provide a vibratory string for a musical instrument having improved harmonics, tonal stability and reduced inharmonicity.
In accordance with one embodiment of the invention a vibratory string is provided constructed of a nickel/titanium alloy material, also known as xe2x80x9cNitinolxe2x80x9d or xe2x80x9cNiTi.xe2x80x9d Such alloys have several peculiar properties that make them particularly advantageous for use in constructing a vibrational string. In particular, the alloys have the unusual ability to reversibly change their crystalline structure from a hard, relatively high-modulus xe2x80x9caustentiticxe2x80x9d crystalline form to a soft, ductile xe2x80x9cmartensiticxe2x80x9d crystalline form upon application of pressure and/or by cooling. This results in a highly elastic material having a very pronounced pseudo-elastic strain characteristic. This pseudo-elastic elastic strain phenomena is characterized by a flattened portion of the stress-strain curve wherein the induced stress remains essentially constant over a relatively large strain (up to about 6%). This unique property is often described as xe2x80x9csuperelasticityxe2x80x9d.
When a musical string is constructed of such a material and stretched to its superelastic state, the tension of the string remains essentially constant regardless of the expansion or contraction of the contacting sound board/bridge against the string and/or the expansion and contraction of the supporting structure. Vibratory strings formed of NiTi alloy wire and properly tensioned also hold a more constant pitch over time than conventional string materials, even when subjected to significant ambient temperature and humidity changes and expansions and contractions of the sound board and supporting structure.
Advantageously, vibrational strings constructed of NiTi wire are less susceptible to xe2x80x9ccreepxe2x80x9d over time. Thus, while conventional steel guitar and piano strings tend to drift down in frequency over time, strings constructed from NiTi wire are found to hold a more constant pitch over long periods of time. Conventional steel wires drift down in frequency over time because of gradual material creep and/or because of plastic strain or stretch in response to temperature and humidity fluctuations. Because of the unique ability of NiTi wire to elastically recover large amounts of strain, vibratory strings constructed of NiTi wire are significantly less susceptible to such effects.
Vibratory strings constructed of NiTi wire are also found to be more robust and less susceptible to corrosion and breakage than strings constructed of conventional materials. Again, because of the ability of NiTi wire to elastically recover large amounts of strain, strings constructed of NiTi wire are found to resist breakage and return to their original shape/pitch even when plucked and strained vigorously and even when exposed to large temperature extremes and corrosive humidity over long periods of time. The large elastic recovery of NiTi wire strings also enables them to vibrate with more energy than strings constructed of conventional materials, such as steel.
While NiTi wires are generally found to be tonally stable over long periods of time, the pitch of a tensioned NiTi wire (depending on the amount of tension applied) can be affected by temperature changes. Surprisingly, however, the temperature response for a NiTi wire is completely reverse to what one normally finds with a vibratory string constructed of conventional materials such as carbon steel. Conventional vibratory strings universally go down in pitch with increasing temperature. Strings constructed of NiTi wire are found to go up in frequency with increasing temperature and vice versa. The exact temperature relationship depends upon the exact alloy material used and the amount of tension applied.
Moreover, by adjusting the tension of a NiTi wire string and/or by combining NiTi alloy(s) and conventional string materials together it is possible to construct a vibratory string having a completely neutral temperature response or an effective thermal expansion coefficient of or about 0.0/xc2x0 C. Such a string would be most useful in many applications requiring high tonal stability in a variety of ambient conditions.
Other salient features and advantages of a vibratory string constructed and used in accordance with the present invention include:
(1) unique and pleasant sound quality
(2) high tonal stability over time (even when xe2x80x9cabusedxe2x80x9d)
(3) tonal stability with temperature/humidity changes
(4) less string breakage (more stretch and forgiveness)
(5) impervious to sweat and humidity
(6) louder sound (more stretch/energy storage)
(7) reduced inharmonicity
In accordance with one embodiment the present invention provides a vibratory string for musical instruments comprising a core formed of one or more filaments or wires of an alloy material selected to have superelastic properties at or about room temperature. The core is impregnated, coated or wound with a second material comprising a precious or semiprecious metal, such as copper, gold, or silver or an alloy thereof.
In accordance with another embodiment the present invention provides a musically tuned vibratory string comprising one or more filaments or wires of an alloy material selected to have superelastic properties at or about room temperature. The vibratory string is secured and supported so as to have an active length thereof capable of sustained vibration. The vibratory string is tensioned or strained to its superelastic state whereby a musical tone may be generated. In a further preferred embodiment the musically tuned vibratory string comprises a Nixe2x80x94Ti alloy wire having a characteristic thermoelastic martensitic phase transformation at a transformation temperature (TT). The string is tensioned or strained to the point of causing at least some stress-induced crystalline transformation from an austenitic crystalline structure to a martensitic crystalline structure.
In accordance with another embodiment the present invention provides a musical instrument strung with one or more vibratory strings comprising a wire formed of an alloy material selected to have superelastic properties at or about room temperature. Optionally, the vibratory strings may be tensioned or strained to their superelastic condition. In a further preferred embodiment, at least one of the vibratory strings comprises a Nixe2x80x94Ti alloy comprising, for example, between about 49.0 to 49.4% Ti and having a characteristic thermoelastic martensitic phase transformation at a transformation temperature (TT) and the string is tensioned or strained to the point of causing stress-induced crystalline transformation from an austenitic crystalline structure to a martensitic crystalline structure.
In accordance with another embodiment the present invention provides a method for stringing a stringed musical instrument. A vibratory string is selected comprising one or more wires formed of an alloy material having superelastic properties at or about room temperature. A first end of the string is then secured to the instrument. A second end of the string is then also secured to the instrument and the string is supported on the instrument so as to provide an active length thereof capable of sustained vibration. Finally, the string is tensioned or strained to its superelastic state. In a further preferred method, the vibratory string is selected to comprise a Nixe2x80x94Ti alloy having a characteristic thermoelastic martensitic phase transformation at a transformation temperature (TT) at or below room temperature and the string is tensioned or strained to the point of causing stress-induced crystalline transformation from an austenitic crystalline structure to a martensitic crystalline structure. In yet a further preferred method, the vibratory string is selected to comprise a Nixe2x80x94Ti alloy having a transformation temperature (TT) between about 15xc2x0 C. and xe2x88x92100xc2x0 C.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.